This invention relates to a dual-system master cylinder assembly useful particularly in vehicle braking systems. The invention relates more particularly to a dual-system master cylinder assembly which compensates for failure of one of the two systems with minimum of stroke loss and without significant increase in stepping force.
As braking devices for automobilies, there is now widely employed dual-system braking arrangements. Such dual-system braking arrangements are often provided with one system specified for front wheel braking and the other system for rear wheel braking, so as to prevent breakdown of the entire brake system due to damage or malfunctioning of a certain part such as brake fluid conduit, hose and the like. A typical example of the master cylinders used in most braking arrangements is the tandem type which includes two pistons, that is, a first piston disposed in the rear part of a cylinder of the uniform diameter, this piston being connected to a push rod and a second piston disposed in the front part of the cylinder. An operating brake fluid chamber and a return spring are interposed between the two pistons.
In this type of master cylinder, however, if one of the brake fluid conduits, hoses and other parts connecting respective outlet ports and front and rear wheel cylinders should be damaged or fail for some reason or the other, the brake stroke is elongated correspondingly, impairing the braking performamce with the result that normal braking operation cannot be effected.
On the other hand, in a stepped type master cylinder a large-diameter piston and a small-diameter piston are formed integral with each other in the inside of a stepped cylinder, so that operating brake fluid feed and discharge from the outlet ports to the front and back braking systems are accomplished simultaneously, but there is inevitably created a certain delicate operational difference between the parts connected to the outlet ports, such as a brake fluid conduit, or hose, or wheel cylinder, brake shoe clearance and the like, for the front wheels and those for the rear wheels. There are also differences in the possibilities of generation of vapor locks, arrangement of accumulators and other conditions, resulting in difference in hydraulic rigidity or brake fluid discharge, so that pressures provided from the two outlet ports undesirably differ from one another.